The present invention relates to a multi-band tuner in which different bands are tuned by different tuning assemblies and in which the selection of the desired tuning assembly to be operative, by applying an energizing voltage thereto, will automatically, by affecting appropriately located voltage-sensitive switching devices such as switching diodes, produce the appropriate electrical connections.
Multi-band tuners have been quite common, particularly in connection with TV reception. Combination VHF-UHF tuners have taken many forms. Sometimes the two tuners are completely independent one from the other, in which case simple switching arrangements are adequate to effect the desired tuner energization and connection. In other instances, in order to minimize the amount of circuitry involved, some portions of the VHF tuner are used in conjunction with the UHF tuner. This complicates the switching arrangement somewhat in connection with selection of one or the other of the tuners to be effective, but because of the simplicity of choices available, the problem has not been particularly troublesome and the instrumentalities employed to effect the switching have presented no problem to the industry.
In recent years, however, and increasingly, a third type of television reception has become prevalent cable television. It has become popular not only in remote areas where commercial television is not readily available, or not readily available in sufficient variety, but also in those areas such as cities, where reception is difficult because of interference or other extraneous factors. It also appeals to many because of the type of programming involved, which can be considerably more mature in nature than that of commercial television. When cable television was in limited demand special tuners for cable television were acceptable, but now that cable television is becoming more generally desired, the need has arisen to provide a single tuning instrumentality capable of detecting and transforming signals either in the VHF, UHF or superband spectrums. Because of the different signal frequencies involved in those three bands or spectrums, the present state of the art mandates using three individual tuning assemblies each usable in only one of those bands or spectrums.
The need to provide three different tuner assemblies in a television set adapted to receive VHF, UHF and superband increases the complexity of the switching arrangements required to energize the desired tuning assembly and prevent the other tuner assemblies from adversely interfering with the operation of the selected assembly. The problems presented are greatly complicated by the economic need to minimize the number of circuits and circuit elements involved, thereby to reduce cost and size and increase reliability. Cable television requires no antenna, but there must be means to introduce the cable signals into the tuner. A section of the existing VHF tuner, such as the normally unused channel 1 section thereof, can be employed to cooperate with the superband tuner in converting the received signal into the viewed television picture. The same channel 1 section is often used in conjunction with UHF tuners, although in a different manner from its use with the superband tuner. Thus as one shifts from one tuner assembly to another there are a significant number of electrical connections which must be shifted.
To accomplish this shifting of electrical connections by means of mechanical switches is of course possible, but not preferred. Mechanical switches are bulky and costly, they require appreciable force to operate, they are often unreliable, and they are comparatively short-lived.
Switching in a fully electrical manner, by means of voltage-sensitive circuit elements such as switching diodes, is known in the art. Electrical switching has the known advantages of speed, small size, low weight, and reliability, as well as the ability to be acted upon from a distance, since all that is required to effect switching is a change in voltage, which can be carried over a lead. However, the very fact that the diodes are actuated by voltage limits their usability, since they can only be incorporated into those circuits where the application of the actuating or switching voltage to the diodes will not adversely affect the main purpose and functions of the circuits involved.
It would be advantageous, particularly from a cost point of view, to provide the VHF signals from the VHF antenna and the superband signals from the cable input at the same node in the television set, but it is by no means obvious how that can be done and at the same time prevent any of the cable television signals from interfering with the VHF signals, or vice versa, when the VHF or superband tuners are respectively rendered operative.
Each of the individual tuner assemblies, to be operative, must be provided with a supply voltage, and for purposes of economy and long life that supply voltage should be applied only to the tuner actually being used and not to the tuners that are not being used at any given point in time.
In accordance with the present invention all of these problems and advantages are harmonized and rendered cooperative and effective through the use of a group of appropriately located and oriented voltage sensitive switching devices such as switching diodes, preferably actuated between connection and disconnection (closed-circuit and open-circuit) conditions by the same selective swtiching means which directs the supply voltage to the particular tuner which it is desired to energize and use at any given time.
The prime object of the present invention is therefore to provide a switching system for a multiband tuning system utilizing a plurality of tuning units, in which the switching is effected by voltage-sensitive switching devices and in which, preferably, the switching voltage is provided by the same instrumentality that provides for energizing that particular tuner.
It is another object of the present invention to provide a tuner capable of tuning at least the VHF and superband areas, and in which a portion of the existing VHF tuner is used in conjunction with one of the other tuners, an effective and efficient voltage-sensitive switching arrangement for selectively energizing the tuner sections and effecting the necessary electrical interconnections to make those tuner sections operative.
It is another object of the present invention to provide, in a combination VHF-superband tuner, a single node to which the VHF and superband signals are delivered, and to provide a voltage-sensitive switching arrangement for ensuring that the superband and VHF signals are delivered to the superband and VHF tuners respectively when those tuners are appropriately energized, without any interference from the non-operative signal.